motors

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jim123

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new castle,de
some motors (3 phase) will say 208/240/480 and give the amps for each . This motor only says 240/480 with the amps for both. I wiring it to 208 , I know the amps will be higher but how do I figure that out ( for my overloads ) and will it affect my service factor on the motor. Another question is my control transformer is 240/480 to 120v there again I have 208 what will the voltage be on the secondary side Thanks
 

iwire

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If the motor was marked 200-230/460 that would mean you could run it on 208 through 240 or reconfigure it for 480.

You say your motor is marked 240/480, are you sure it does not say 230/460? Motors are general labeled just a bit lower than the service voltage.

Anyway, code wise if is not marked 200 or 208 it should not be connected to 208.

There is no NEC compliant way to determine the overload size either.

Then there is the small chance that 208 will not provide enough starting torque to get the unit turning.

The control voltage would drop to about 104 volts which could be a problem.

I would likely get a couple of buck boost transformers and boost the 208 closer too 240. That solves the low control voltage you would get.
 

GoldDigger

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If your service is wye, as is most likely with 208V line to line, you will need three boost transformers to do the job.
If you have a corner grounded delta, you can use just two boost transformers.
 

GoldDigger

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I have never needed more than two transformers to boost 208 three phase to 230 three phase.
Just how do you do that and keep voltage balance in your wye? Or do you consider an unbalanced wye good enough for a delta connected motor? As you implied, you might not get all the way to 240 on each phase that way, and will still have an unbalanced delta, even without a neutral going to the motor.
 

iwire

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Just how do you do that and keep voltage balance in your wye? Or do you consider an unbalanced wye good enough for a delta connected motor? As you implied, you might not get all the way to 240 on each phase that way, and will still have an unbalanced delta, even without a neutral going to the motor.

You lost me.

With two buck boosts I can get about 236 line to line on all phases.

Line to ground, or neutral will be 120 / 135 / 135 or so but not an issue.
 

GoldDigger

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You lost me.

With two buck boosts I can get about 236 line to line on all phases.

Line to ground, or neutral will be 120 / 135 / 135 or so but not an issue.
Good enough sounds good enough for me, I guess.

But with 120/135/135 in wye, the line to line voltages will not be equal. The voltage between the two 135 legs will be greater than the other two pairs and the phase angles will not be exactly 120 degrees, either.
I have not worked out the actual numbers, though.
The voltage errors will be greater than for any reasonable POCO tolerance, so the reaction of the motor would not have been specifically tested.
 

iwire

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GoldDigger

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iwire

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Your link recommends two boosts for three phase three wire and three boost pots for three phase four wire. Are they talking about using the service input or the wired load to choose which to use?

TTBOMK it is the load you are supplying that matters. I hope so as I have installed or specified a good number of these. :eek:hmy:

A common application for me is refrigerated semi-trailer units that are 230-240 3 phase and often the overloads will trip when supplied by 208.

Others have been air compressors and Slurpee machines. The Slurpee machines come with multiple dire warnings to the electrical contractor about input voltage range and how it would be verified at start up. They take their junk food serious.
 

ActionDave

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You two are free to carry on without me, I'll just jump in and say, depending on the application I would be inclined to hook up the motor with the existing 208V, set the overloads at 115% of the name plate and see how it goes before getting a buck/boost....or two, or three if needed......
 

iwire

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You two are free to carry on without me, I'll just jump in and say, depending on the application I would be inclined to hook up the motor with the existing 208V, set the overloads at 115% of the name plate and see how it goes before getting a buck/boost....or two, or three if needed......

You mean the smoke test?

Give it shot and if the motor smokes it fails?

Sure, that is always an option. :lol:

Do two buck boosts cost more than a smoked motor, downtime cost and maybe the OT to repair?
 

ActionDave

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TTBOMK it is the load you are supplying that matters. I hope so as I have installed or specified a good number of these. :eek:hmy:

A common application for me is refrigerated semi-trailer units that are 230-240 3 phase and often the overloads will trip when supplied by 208.
Very finicky about their voltage those refer units are, nice and loud too.

Others have been air compressors and Slurpee machines. The Slurpee machines come with multiple dire warnings to the electrical contractor about input voltage range and how it would be verified at start up. They take their junk food serious.
I have worked on those Slurpee machines. They are far more complex than that cartoon dog and ugly colors would lead one believe.....takes some of the sting out of paying $12 to $15 buying a treat for my kids and maybe their friends.
 

ActionDave

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You mean the smoke test?

Give it shot and if the motor smokes it fails?

Sure, that is always an option. :lol:

Do two buck boosts cost more than a smoked motor, downtime cost and maybe the OT to repair?
I'm a brave adventurous sort.

Also, I have seen many 230V motors do fine on 208V. Put one in for a compressor on a car wash three years ago. No trouble to date.
 

GoldDigger

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I'm a brave adventurous sort.

Also, I have seen many 230V motors do fine on 208V. Put one in for a compressor on a car wash three years ago. No trouble to date.
As pointed out in some other threads (by jraef, IIRC), a nominal to high 208 volt service falls within the range of allowed voltage for a nominal 230V motor. But if the supply voltage drops toward the lower end of the range for a nominal 208V, it drops below the minimum voltage for 230V.
Hence the problem. A motor specified for 200/230 has a design margin for the lower voltage higher current mode.
And as also suspected by the OP the broad voltage range may affect the service factor rating of the motor.
 

iwire

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I'm a brave adventurous sort.

Also, I have seen many 230V motors do fine on 208V. Put one in for a compressor on a car wash three years ago. No trouble to date.

Of course, it might work. I would even say it is likely to work.

On the other hand it may not work, it is not right and if you do this as an EC you may end up eating the cost of a new motor instead of making money installing transformers.
 

Besoeker

Senior Member
Location
UK
If your service is wye, as is most likely with 208V line to line, you will need three boost transformers to do the job.
If you have a corner grounded delta, you can use just two boost transformers.
Why not just one three-phase unit?
I've done that often enough where we have had systems on a non-standard voltage.
Typically, our electronics is a standard design for 400/3/50 but sometimes the power side is a different voltage - sometimes higher, sometimes lower.
It is generally more convenient to do that that provide non-standard electronics and it avoids potential confusion when it comes to supplying and setting up spares.
 
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